[runtime] Be a bit more explicit about format warnings related to security. (#14165)

Make.config

@@ -288,7 +288,7 @@ IOS_CXX=$(XCODE_CXX)
 SIMULATOR_BIN_PATH=$(XCODE_DEVELOPER_ROOT)/Platforms/iPhoneSimulator.platform/Developer/usr/bin
 SIMULATOR_CC=$(IOS_CC)
 
-CFLAGS= -Wall -fms-extensions -Werror -Wconversion -Wdeprecated -Wuninitialized -fstack-protector-strong
+CFLAGS= -Wall -fms-extensions -Werror -Wconversion -Wdeprecated -Wuninitialized -fstack-protector-strong -Wformat -Wformat-security -Werror=format-security
 
 ifdef ENABLE_BITCODE_ON_IOS
 BITCODE_CFLAGS=-fembed-bitcode-marker